1. Field of the Invention
The invention relates to a vehicle seat.
2. Description of Related Art
A typical vehicle seat (hereinafter simply referred to as a “seat” where necessary) provided in a vehicle such as an automobile has a seat cushion that serves as a seat portion for an occupant and a seat back that supports the back of the occupant. In addition, seat slide rail mechanisms capable adjusting the position of the seat with respect to a vehicle floor are installed between the floor and the seat as seat support members on the side of the floor. The seat slide rail mechanisms are configured such that upper rails disposed on the side of the seat cushion fit in lower rails disposed on the side of the floor to be slidably movable. Such a vehicle seat is described in, for example, Japanese Patent Application Publication No. 2011-42221 (JP 2011-42221 A) and Japanese Patent Application Publication No. 2013-2220784 (JP 2013-2220784 A).
The seat cushion and the seat slide rail mechanisms of the seat having the seat slide rail mechanisms as described above are joined together when side frames that form the frame of the seat cushion and the upper rails of the seat slide rail mechanisms are joined together by joining brackets. At this time, the joining between the side frames and the joining brackets is typically performed by welding connection, and the joining between the upper rails and the joining brackets is performed by fastening units, each of which is constituted by a bolt and a nut, for example.
The side frames of the seat cushion and the upper rails of the seat slide rail mechanisms may be disposed offset from each other in the width direction (right-left direction) of the seat cushion. That is, the upper rails of the seat slide rail mechanisms may be disposed on the outer side or the inner side of the side frames of the seat cushion.
In a case in which the side frames of the seat cushion and the upper rails of the seat slide rail mechanisms are disposed offset from each other as described above, torsional deformation may be caused in the joining brackets that join the side frames and the upper rails together when an abnormal force due to an external force is applied to the side frames of the seat cushion.
Specifically, when the vehicle is struck by the following vehicle from behind (rear-side collision), a force is applied by the impact of the rear-side collision to the seat of the vehicle to relatively move the seat rearward. The force is also applied to the side frames of the seat cushion and even to the joining brackets joined to the side frames. By the force applied to the joining brackets, the joining brackets are rotated about portions at which the joining brackets are fastened to the upper rails to cause torsional deformation. When the torsional deformation is caused with the rotation of the joining brackets, the side frames are greatly deformed, which negatively affects a rearward tilting angle of the seat. Thus, the seat may sink down as a whole.
As a countermeasure for reducing the torsional deformation of the joining brackets at the rear-side collision described above, fastening units that fasten the joining brackets and the upper rails to each other may be disposed at a plurality of portions. However, disposing the fastening units at the plurality of portions makes the fastening configuration of the vehicle seat complicated correspondingly, which results in an increase in the cost and the mass of the vehicle seat.